This invention relates to a medical or surgical stapler.
As disclosed in U.S. Pat. No. 4,411,378, a medical stapler includes a casing having an opening. The inner surfaces of those portions of the casing disposed immediately adjacent respectively to the opposite side edges of the opening serve respectively as retaining surfaces for a staple. First and second guide members, extending respectively along straight lines intersecting each other, are provided within the casing. A ram is slidably supported on the first guide member. An anvil extends from the distal end of the second guide member. The anvil is disposed in the vicinity of the opening of the casing, and is disposed in a path of movement of the ram. The ram has first shaping surfaces at its distal end, and the anvil has a second shaping surface disposed in opposed relation to the ram. The second shaping surface of the anvil is disposed perpendicular to the path of movement of the ram. A number of staples are slidably supported on the second guide member, and are arranged in contiguous relation to one another in the direction of the length of the second guide member. Each of the staples has a crown portion, and a pair of legs formed respectively at the opposite ends of the crown portion. A spring, provided within the casing, pushes a rearmost one of a number of staples, supported on the second guide member, to urge these staples toward the anvil. When an operating member, mounted on the casing, is operated to advance the ram, the foremost staple is shaped through the cooperation of the ram with the anvil in such a manner that the pair of legs thereof are moved toward each other, and during this shaping operation, a required portion of a patient is sutured.
In the medical stapler of the above U.S. Patent, during the shaping of the foremost staple, the crown portion thereof rolls on the second shaping surface of the anvil, and therefore there is a possibility that a satisfactory suturing may not be achieved. More specifically, the anvil is fixedly mounted on the casing, but the ram is supported on the first guide member with a slight play in a direction perpendicular to the path of movement of the ram in order to ensure a smooth sliding movement of the ram. During the shaping of the foremost staple, the upper portion of the crown portion thereof is contacted with the first shaping surfaces of the ram under a large force, whereas the lower portion of the crown portion is contacted with the second shaping surface of the anvil under a large force. The crown portion of the foremost staple receives the force of the above spring via the crown portions of the subsequent staples; however, since the legs of the foremost staple are abutted against the retaining surfaces of the casing, the crown portion is prevented from rolling. When the shaping of the foremost staple further proceeds, so that the legs of the foremost staple are disengaged from the retaining surfaces, the crown portion may roll on the second shaping surface, because the crown portion of the foremost staple is urged by the crown portions of the subsequent staples, and the ram is moved by an amount corresponding to the above play.
U.S. Pat. No. 4,261,244 discloses a stapler in which a V-shaped groove, which is disposed perpendicular to a path of movement of a ram and extends parallel to a crown portion of each staple, is formed in each of first shaping surfaces of the ram. Each staple has a polygonal cross-section. When the foremost staple is to be shaped, the upper portion of the crown portion thereof is received in the V-shaped grooves. In this conventional stapler, the rolling of the foremost staple can be prevented, but the manufacturing cost of the staple having a polygonal cross-section is high. If staples of a circular cross-section are used, there is a possibility that the upper portion of the crown portion of the foremost staple may slip in the V-shaped grooves, thereby inviting a possibility that the crown portion may roll on a second shaping surface of an anvil.
U.S. Pat. Nos. 4,582,237 and 4,662,555 disclose staplers in which a groove for receiving an upper portion of a crown portion of a foremost staple is formed in each of first shaping surfaces of a ram.
Some of the inventors of the present invention earlier developed a stapler disclosed in U.S. Pat. No. 5,022,579, and this stapler resembles the stapler of the present invention, but does not have the features of the present invention.